Rotating systems such as rotating shafts oftentimes experience torsional vibration as well as translational vibration. Generally speaking, torsional vibration refers to the vibration which results in oscillatory rotation of the rotating component (e.g., rotating shaft) about its central longitudinal axis. Translational vibration, on the other hand, generally refers to the vibration which results in movement of the rotating component in a direction normal to its central longitudinal axis.
In a wide variety of different systems such as engines for automobiles, jet skis and the like, torsional vibration as well as translational vibration are present. In the case of engines, for example, the torsional vibration and the translational vibration can be attributed to the motion of sliding and rotating masses that constitute various parts of the engine. These masses include pistons, connecting rods, crank throws and the like. In addition to the motion of the sliding and rotating masses, the combustion processes in these cylinders during operation of the engine can contribute to the creation of torsional vibration and translational vibration.
Proposals have been made in the past to employ untuned viscous torsional dampers in an attempt to reduce torsional vibration. FIG. 1 illustrates such an untuned viscous torsional damper in the context of a pulley. The pulley 30 is rotatably driven by a shaft 31 and is provided with a cylindrical cavity that contains a disk-damping mass 32. The space between the inner walls of the cavity in the pulley 30 and the outer surface of the damping mass 32 defines a shear gap, and this shear gap is typically filled with a suitable viscous fluid which is selected to maximize the torsional damping for a specified ratio of the inertia of the pulley 30 versus the inertia of the damping mass 32. The amount of shear damping that occurs in the shear gap between the pulley 30 and the damping mass 32 depends on the size of the space, the viscosity of the fluid and the relative rotational speed between the pulley and the damping mass.
While the untuned viscous damper mentioned above may be capable of offsetting some torsional vibration, it suffers from a variety of disadvantages and drawbacks. In one respect, the untuned viscous damper is not designed to address translational vibration that results from movement of the rotating shaft in a direction normal to the central longitudinal axis of the shaft. As a result, there still exists an out of balance condition in the system which can adversely affect the operation, performance and life of the system.
A need also exists for a device that removes both translational and torsional vibration, yet which is also relatively small and compact in design so that the device can be used in conjunction with existing machines and systems.